Fluid extraction systems use a process fluid under controlled temperature and pressure conditions to extract an extracted material from a source material. For example, carbon dioxide (CO2) in a supercritical or liquid state can be used as one such process fluid to extract botanical oils and resins from a botanical source material. Other process fluids, including CO2 mixed with certain additives, can optionally be used. Fluid extraction systems can also be used to operate on a variety of source material to extract a variety of extracted materials known in the art.
For example, U.S. Pat. No. 9,132,363 (Joseph) describes an extraction apparatus comprising an extraction vessel configured to remove an extracted material from a source material in contact with a process fluid to form a mixture. The apparatus further comprises a separation chamber and a process fluid circulation conduit, the conduit comprising a separation portion configured to receive the mixture and permit a portion of the extracted material to separate from the mixture within the separation chamber. The apparatus further comprises a temperature regulator configured to permit re-circulation of a temperature regulation fluid and regulate the temperature of the process fluid.
The properties of the process fluid in such an extraction system will dictate its phase at a given combination of temperature and pressure, as may be shown on a conventional phase diagram. Taking CO2 process fluid as an example, for CO2 to be maintained in a supercritical state, a temperature of at least 87.98 degrees Fahrenheit and a pressure of at least 1,071 PSI (conventionally known as CO2's supercritical point) is necessary. Following the CO2 phase diagram, gaseous CO2 can be condensed to liquid or vaporized back to a gas along a continuum. Generally, CO2 requires greater pressure to be maintained as a liquid at higher temperatures. Conversely, to maintain CO2 as a gas at relatively low temperatures, the pressure also must be relatively low. Also, when CO2 decompresses, a phenomena known as Joule-Thompson cooling occurs. Conversely, when CO2 is compressed, its temperature increases.
CO2 has solvency power when in liquid and supercritical states, allowing it to form a mixture with an extracted material when placed in contact with a source material. One method of separating the extracted material from the mixture is to pass the mixture from the extraction vessel to a separation chamber and decompress the mixture such that the CO2 changes to a gas and loses its solvency power. Low pressure within the separation chamber for effective separation implies low temperature as well.
The problem then becomes how to efficiently recirculate the CO2 back to the extraction vessels at an optimal pressure and temperature for a desired extraction, which will be at a relatively higher temperature and relatively higher pressure than the CO2 has when exiting the separation chamber.